Prior to 'Manhunt', the majority of films about the French Resistance, certainly in Britain and America, were very simplistic boy's own adventure stuff about plucky men (and sometimes women), with little exploration of the issues relating to collaboration and resistance. 'Manhunt' changed all that.
Of course, it helped that it had literate scripts, fascinating characters, and superb performances. It was an instant T.V. 'hit'. But it was a superb history lesson. It showed the resistance movement as a collection of individuals with a variety of motives - Communists, Gaullists, evaders from labour service, and people with personal motives. They distrusted each other sometimes, and saw other groups as rivals. Similarly, the Germans were not monolithic. The S.S. and Gestapo hated the Abwere, and vice versa.
The most interesting character was Graz, the Abwhere intelligence officer, for he was on the fringe of the anti-Nazi resistance movement.
Consequently, you never really knew what happened from one episode to the next. That was what made it so exciting and watchable.
The series proved so popular that it was extended beyond the anticipated number of episodes.
In many ways 'Manhunt' prefigures themes in 'Army of Shadows' and 'Soldier of Orange'.